Highly esterified oligosaccharide polyester lubricant for machinery

ABSTRACT

A method is provided for reducing friction between at least two metal surfaces which are in a frictional relationship with each other or otherwise in need of lubrication. The method includes contacting the metal surfaces with an effective amount of a lubricant composition comprised of partially-esterified sucrose molecules having, in one embodiment, an average distribution of from 5 to 7 fatty acids bound to a sucrose backbone. The lubricant may also include from about 20 ppm to about 10,000 ppm of an antioxidant, about half of which may be an active tocopherol.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application Ser. No. 61/024,363 filed Jan. 29, 2008, incorporated by reference herein.

FIELD OF THE INVENTION

This disclosure relates to lubricants for use with the moving parts of various types of machinery, and in particular, with air-driven tools and equipment.

BACKGROUND OF THE INVENTION

Various lubricants have been used for parts of machinery that rub or rotate to reduce friction and wear. Metal surfaces can become very hot during use. Lubricants also act as a coolant for the metal. An effective lubricant reduces the abrasion and friction caused by the rotating or rubbing motions of the working parts of machinery. Lubricants are also applied to working machine surfaces to fill in any depressions in uneven surfaces and thereby form a smoother surface thereby reducing the resistance or friction between adjacent surfaces.

Lubricants have also been introduced into the air flow of pneumatic tools for lubricating the motor or other parts of the tool. Pneumatic tools generally have a pneumatic motor connected by some kind of coupling to a drive member for driving the operative portion of the tool. The motor housing is typically connected to a source of fluid under pressure, such as compressed air, to drive the motor. By introducing the lubricant into the compressed air flow, the lubricant is continually fed to the moving parts of the motor when it is in use. Pneumatic or air-driven tools are used in many industries, such as mining, construction, hydro electric facilities, industrial manufacturing and production lines, such as in control valves and moving cylinders.

Typical lubricants have consisted of petroleum based oils and greases or vegetable based oils, sometimes in combination with various pulverized metallic, ceramic or organic compounds. There are problems with these products. Rock drill greases, for example, do not lubricate as well as oils in overhead bolting & drilling. They have a moderate viscosity index, which means they thin out rapidly. Rock drill greases have an unpleasant odor and are not biodegradable. Finally, they have poor thermal heat transfer capabilities.

Petroleum based products also present problems for workers due to the generation of oil particulate mists, known as fogging. When used in enclosed spaces, such as in mines and tunnels where the air flow is limited to begin with, the particulate material has little opportunity to dissipate. The permissible exposure limit for petroleum based rock drill oils and greases, for example, is 5 ppm.

With pneumatic tools, petroleum based oil lubricants can reduce the useful life of the tool. The rotating or sliding parts of machines using such lubricants tend to wear and heat up over long periods of use leading eventually to the deterioration or loss of effectiveness of the lubricant. Water in the compressed air thins out the oil and causes the tool surfaces to wear faster if not frequently replaced. Petroleum based lubricants also leave a slippery deposit on tool surfaces making handling the tools difficult. Like rock drill greases, they are not biodegradable and can pollute water sources. Petroleum based lubricants are also very dirty to use, leaving black deposits on workers' skin and clothing. Further, with rising oil prices, uncertain supplies and the global environmental risks they pose, the cost of petroleum based oils and greases is prohibitive and can only be expected to increase over time.

To combat some of these problems, vegetable oil based rock drill oils have been used as lubricants. Examples include castor oil and canola oil. They are not without their own problems. Vegetable oil based rock drill oils have low viscosities, also produce fogging, do not work well or at all in many standard lubricators, have an unusual odor, and have poor oxidative stability.

There is a need for a lubricant that avoids some if not all of these problems.

SUMMARY OF THE INVENTION

A new lubricating composition has been discovered in the form of partially-esterified oligosaccharide. A method for reducing friction between at least two metal surfaces which are in a frictional relationship with each other is described herein which includes contacting the metal surfaces with an effective amount of a lubricant composition comprised of partially-esterified oligosaccharide molecules.

In one embodiment of the method when used to lubricate pneumatic tools and equipment, the metal surfaces are contacted by introducing the lubricant into the flow of compressed air in the pneumatic tool, or equipment.

In another embodiment of the method the metal surfaces are contacted by applying the lubricant directly to the metal surfaces in need of lubrication.

An embodiment of the lubricant may comprise partially-esterified sucrose. Each partially-esterified sucrose molecule of this embodiment of the lubricating composition comprises a sucrose backbone having from 5 to 7 fatty acids bound thereto. Each fatty acid bound to the sucrose backbone may have from 2 to 28, and preferably from 4 to 22, carbon atoms in unbranched or branched chains saturated and unsaturated and mixtures thereof. In one embodiment of the lubricating composition, the partially-esterified sucrose molecules have an average distribution of five to six or six to seven fatty acids bound thereto. In another embodiment of the lubricant composition, the partially-esterified sucrose molecules have an average distribution of six fatty acids bound thereto.

The lubricating composition may further include an amount of an antioxidant effective for reducing the rate of oxidation of the lubricant. The amount useful in some embodiments of the lubricant may range from about 20 ppm to about 10,000 ppm. Other embodiment may use from about 100 ppm to about 5000 ppm, or from about 500 ppm to about 2500 ppm of the antioxidant. An amount found to be useful in at least one embodiment of the lubricant is about 1000 ppm of the antioxidant. In at least one embodiment of the lubricating composition, at least half of the antioxidant is an active tocopherol.

BRIEF DESCRIPTION OF THE DRAWINGS

The various embodiments set forth in the Description of the Invention will be better understood with reference to the following non-limiting drawings, wherein:

FIG. 1 is a schematic comparison of the applicant's understanding of the behavior of the lubricating film of the present invention and that of a prior art petroleum-based oil lubricant.

FIG. 2 is a schematic of an exemplary process for making an embodiment of the partially-esterified lubricant of the invention.

DETAILED DESCRIPTION OF THE INVENTION A. Definitions

As used herein, the term “comprising” means various components conjointly employed in the preparation of the compositions of the present disclosure. Accordingly, the terms “consisting essentially of” and “consisting of” are embodied in the term “comprising”.

As used herein, the term “partially-esterified sucrose” represents a commercially distinct chemical class (chemical compound) known as sucrose esters of fatty acids (SEFA). SEFA compounds are high molecular weight compounds formed by esterifying fatty acids to a sucrose molecule backbone, which contains eight potential esterification sites. A fully esterified sucrose has eight esters bound to the sucrose backbone. A partially esterified-sucrose has fewer than eight esters bound thereto. The fatty acids used to form these esters include those containing about four to 28 or more carbon atoms, and preferably containing from 8 to about 22 carbon atoms, and mixtures of such esters. Suitable esters can be prepared by the reaction of diazoalkanes and fatty acids, or derived by alcoholysis from the fatty acids naturally occurring in fats and oils. Fatty acid esters suitable for use herein may be derived from either saturated or unsaturated fatty acids. Suitable preferred saturated fatty acids include, for example, capric, lauric, palmitic, stearic, behenic, isomyristic, isomargaric, myristic, caprylic, and anteisoarachadic. Suitable preferred unsaturated fatty acids include, for example, maleic, linoleic, licanic, oleic, linolenic, and erydiogenic acids. Mixtures of fatty acids derived from soybean oil, palm oil, coconut oil, and cottonseed are especially preferred for use herein. Methyl esters are the preferred fatty acid esters for use herein, since their use in the lubricant described herein tends to result in high yields of sucrose fatty acid partially-esterified reaction products.

Sucrose is an oligosaccharide. Other oligosaccharides believed to be suitable for use herein include, for example, maltose, kojibiose, nigerose, cellobiose, lactose, melibiose, gentiobiose, turanose, rutinose, trehalose, and raffinose. Also believed to be useful are the polyols, which include for example, sorbitol and others.

As used herein, “average distribution” with respect to fatty acids, means the average frequency of fatty acids bound to the sucrose backbone of a quantity of partially-esterified sucrose molecules, which includes individual sucrose molecules having a lesser or greater number of esters bound thereto, but when taken together, have a number of fatty acids bound to the sucrose backbone, which on average equal the range or number stated herein.

As used herein, all parts, percentages, and ratios are based on weight unless otherwise specified.

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical value recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm”.

B. Description of Various Embodiments of the Invention

The lubricant of the present invention is made of a partially-esterified oligosaccharide composition, preferably in combination with an antioxidant additive. Machine parts and particularly pneumatic, or air-driven, machine parts are coated with the lubricant to reduce friction and wear. The lubricant has been found to be particularly advantageous in pneumatic equipment where the lubricant is introduced into the compressed air flow for lubricating the motor or other parts of the tool. As the experiments described herein will show, it has been discovered that a lubricant comprised of partially-esterified sucrose, in addition to providing excellent lubrication for metal surfaces, also provides surprising and unexpected benefits to the environment and to the safety of workers whose jobs require them to use, or be in the vicinity of, lubricated machinery. Other advantages of the various embodiments of the lubricant of the present invention will be apparent to those skilled in the art.

A preferred partially-esterified sucrose has an average distribution of fatty acid esters on the sucrose backbone of 5 to 7, wherein the fatty acid moieties each contain 4 or more, and preferably from 4 to about 28 carbon atoms, more preferably from 8 to 22 carbon atoms and most preferably contain 18 carbon atoms. A particularly preferred partially-esterified sucrose is the hexa-ester of sucrose in which there are 6 fatty acid moieties in the molecule.

The partially-esterified sucrose may be combined with an anti-oxidant. The antioxidants useful for the lubricant additive include tocopherols, alkylated monophenols, alkylthiomethylphenols, alkylidenebisphenols, hydroxylated thiodiphenyl ethers, hydroquinones and alkylated hydroquinones, hydroxybenzylated malonates, benzyl compounds, aromatic hydroxybenzyl compounds, triazine compounds, benzyl phosphonates, acylaminophenols, ascorbic acid, certain esters, and aminic antioxidants.

In one embodiment, the antioxidant is a tocopherol. Examples of tocopherols include α-tocopherol, β-tocopherol, γ-tocopherol, δ-tocopherol and mixtures thereof (vitamin E).

Examples of alkylated monophenols include 2,6-di-tert-butyl-4-methylphenol, 2-tert-butyl-4,6-di-methylphenol, 2,6-di-tert-butyl-4-ethylphenol, 2,6-di-tert-butyl-4-n-butylphenol, 2,6-di-tert-butyl-4-isobutylphenol, 2,6-dicyclopentyl-4-methylphenol, 2-(α-methylcyclohexyl)-4,6-dimethyl-phenol, 2,6-dioctadecyl-4-methylphenol, 2,4,6-tricyclohexylphenol, 2,6-di-tert-butyl-4-methoxymethylphenol, nonylphenols which are linear or branched in the side chains, for example, 2,6-di-nonyl-4-methylphenol, 2,4-dimethyl-6-(1′-methylundec-1′-yl)phenol, 2,4-dimethyl-6-(1′-methylheptadec-1′-yl)phenol, 2,4-dimethyl-6-(1′-methyltridec-1′-yl)phenol and mixtures thereof.

Examples of alkylthiomethylphenols include 2,4-dioctylthiomethyl-6-tert-butylphenol, 2,4-dioctylthiomethyl-6-methylphenol, 2,4-dioctylthiomethyl-6-ethylphenol, 2,6-di-dodecylthiomethyl-4-nonylphenol.

Examples of hydroquinones and alkylated hydroquinones include 2,6-di-tert-butyl-4-methoxy-phenol, 2,5-di-tert-butylhydroquinone, 2,5-di-tert-amylhydroquinone, 2,6-diphenyl-4-octadecyloxyphenol, 2,6-di-tert-butylhydroquinone, 2,5-di-tert-butyl-4-hydroxyanisole, 3,5-di-tert-butyl-4-hydroxyanisole, 3,5-di-tert-butyl-4-hydroxyphenyl stearate, bis(3,5-di-tert-butyl-4-hydroxyphenyl)adipate.

Examples of hydroxylated thiodiphenyl ethers include 2,2′-thiobis(6-tert-butyl-4-methylphenol), 2,2′-thiobis(4-octylphenol), 4,4′-thiobis(6-tert-butyl-3-methylphenol), 4,4′-thiobis(6-tert-butyl-2-methyl phenol), 4,4′-thiobis(3,6-di-sec-amylphenol), 4,4-bis(2,6-dimethyl-4-hydroxyphenyl)disulfide.

Examples of alkylidenebisphenols include 2,2′-methylenebis(6-tert-butyl-4-methylphenol), 2,2′-methylenebis(6-tert-butyl-4-ethylphenol), 2,2′-methylenebis[4-methyl-6-α-methylcyclohexyl)-phenol], 2,2′-methylenebis(4-methyl-6-cyclohexylphenol), 2,2′-methylenebis(6-nonyl-4-methyl phenol), 2,2′-methylenebis(4,6-di-tert-butylphenol), 2,2′-ethylidenebis(4,6-di-tert-butyl-phenol), 2,2′-ethylidenebis(6-tert-butyl-4-isobutylphenol), 2,2′-methylenebis[6-(α-methylbenzyl)-4-nonylphenol], 2,2′-methylenebis[6-(α,α-dimethylbenzyl)-4-nonylphenol], 4,4′-methylenebis(2,6-di-tert-butylphenol), 4,4′-methylenebis(6-tert-butyl-2-methylphenol), 1,1-bis(5-tert-butyl-4-hydroxy-2-methylphenyl)butane, 2,6-bis(3-tert-butyl-5-methyl-2-hydroxybenzyl)-4-methylphenol, 1,1,3-tris(5-tert-butyl-4-hydroxy-2-methylphenyl)butane, 1,1-bis(5-tert-butyl-4-hydroxy-2-methyl-phenyl)-3-n-dodecylmercaptobutane, ethylene glycol bis[3,3-bis(3′-tert-butyl-4′-hydroxyphenyl)butyrate], bis(3-tert-butyl-4-hydroxy-5-methyl-phenyl)dicyclopenta-diene, bis[2-(3′-tert-butyl-2′-hydroxy-5′-methylbenzyl)-6-tert-butyl-4-methylphenyl]terephthalate, 1,1-bis-(3,5-dimethyl-2-hydroxyphenyl)butane, 2,2-bis(3,5-di-tert-butyl-4-hydroxyphenyl)propane, 2,2-bis(5-tert-butyl-4-hydroxy-2-methylphenyl)-4-n-dodecylmercaptobutane, 1,1,5,5-tetra-(5-tert-butyl-4-hydroxy-2-methylphenyl)pentane.

Examples of benzyl compounds include 3,5,3′,5′-tetra-tert-butyl-4,4′-dihydroxydibenzyl ether, octadecyl-4-hydroxy-3,5-dimethylbenzylmercaptoacetate, tridecyl-4-hydroxy-3,5-di-tert-butylbenzylmercaptoacetate, tris(3,5-di-tert-butyl-4-hydroxybenzyl)amine, bis(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)dithioterephthalate, bis(3,5-di-tert-butyl-4-hydroxy-benzyl)sulfide, isooctyl-3,5-di-tert-butyl-4-hydroxybenzylmercaptoacetate.

Examples of hydroxybenzylated malonates include dioctadecyl-2,2-bis(3,5-di-tert-butyl-2-hydroxybenzyl)malonate, di-octadecyl-2-(3-tert-butyl-4-hydroxy-5-methylbenzyl)malonate, di-dodecylmercaptoethyl-2,2-bis(3,5-di-tert-butyl-4-hydroxybenzyl)malonate, bis[4-(1,1,3,3-tetramethylbutyl)phenyl]-2,2-bis(3,5-di-tert-butyl-4-hydroxybenzyl)malonate.

Examples of aromatic hydroxybenzyl compounds include 1,3,5-tris(3,5-di-tert-butyl-4-hydroxy-benzyl)-2,4,6-trimethylbenzene, 1,4-bis(3,5-di-tert-butyl-4-hydroxybenzyl)-2,3,5,6-tetramethylbenzene, 2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)phenol.

Examples of triazine compounds include 2,4-bis(octylmercapto)-6-(3,5-di-tert-butyl-4-hydroxy-anilino)-1,3,5-triazine, 2-octylmercapto-4,6-bis(3,5-di-tert-butyl-4-hydroxyanilino)-1,3,5-tri-azine, 2-octylmercapto-4,6-bis(3,5-di-tert-butyl-4-hydroxyphenoxy)-1,3,5-triazine, 2,4,6-tris-(3,5-di-tert-butyl-4-hydroxyphenoxy)-1,2,3-triazine, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate, 1,3,5-tris(4-tert-butyl-3-hydroxy-2,6-dimethylbenzyl)isocyanurate, 2,4,6-tris(3,5-di-tert-butyl-4-hydroxyphenylethyl)-1,3,5-triazine, 1,3,5-tris(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)-hexahydro-1,3,5-triazine, 1,3,5-tris(3,5-dicyclohexyl-4-hydroxy benzyl)isocyanurate.

Examples of benzyl phosphonates include dimethyl-2,5-di-tert-butyl-4-hydroxybenzylphosphonate, diethyl-3,5-di-tert-butyl-4-hydroxybenzylphosphonate, dioctadecyl 3,5-di-tert-butyl-4-hydroxybenzylphosphonate, dioctadecyl-5-tert-butyl-4-hydroxy-3-methylbenzylphosphonate, the calcium salt of the monoethyl ester of 3,5-di-tert-butyl-4-hydroxybenzylphosphonic acid.

Examples of acylaminophenols include 4-hydroxylauranilide, 4-hydroxystearanilide, octyl N-(3,5-di-tert-butyl-4-hydroxyphenyl)carbamate.

Examples of esters follow. Esters of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid with mono- or polyhydric alcohols, e.g. with methanol, ethanol, n-octanol, i-octanol, octadecanol, 1,6-hexanediol, 1,9-nonanediol, ethylene glycol, 1,2-propanediol, neopentyl glycol, thiodiethylene glycol, diethyllene glycol, triethylene glycol, pentaerythritol, tris(hydroxyethyl)isocyanurate, N,N′-bis(hydroxyethyl)oxamide, 3-thiaundecanol, 3-thiapentadecanol, trimethylhexanediol, trimethylol-propane, 4-hydroxymethyl-1-phospha-2,6,7-trioxabicyclo[2.2.2]octane. Esters of β-(5-tert-butyl-4-hydroxy-3-methylphenyl)propionic acid with mono- or polyhydric alcohols, e.g. with methanol, ethanol, n-octanol, i-octanol, octadecanol, 1,6-hexanediol, 1,9-nonanediol, ethylene glycol, 1,2-propanediol, neopentyl glycol, thiodiethylene glycol, diethylene glycol, triethylene glycol, pentaerythritol, tris(hydroxyethyl)isocyanurate, N,N′-bis(hydroxyethyl)oxamide, 3-thiaundecanol, 3-thiapentadecanol, trimethylhexanediol, trimethylolpropane, 4-hydroxymethyl-1-phospha-2,6,7-trioxabicyclo[2.2.2]octane; 3,9-bis[2-{3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionyloxy}-1,1-dimethylethyl]-2,4,8,10-tetraoxaspiro[5.5]undecane. Esters of β-(3,5-dicyclohexyl-4-hydroxyphenyl)propionic acid with mono- or polyhydric alcohols, e.g. with methanol, ethanol, octanol, octadecanol, 1,6-hexanediol, 1,9-nonanediol, ethylene glycol, 1,2-propanediol, neopentyl glycol, thiodiethylene glycol, diethylene glycol, triethylene glycol, pentaerythritol, tris(hydroxyethyl)isocyanurate, N,N′-bis(hydroxyethyl)oxamide, 3-thiaundecanol, 3-thiapentadecanol, trimethylhexanediol, trimethylolpropane, 4-hydroxymethyl-1-phospha-2,6,7-trioxabicyclo[2.2.2]octane. Esters of 3,5-di-tert-butyl-4-hydroxyphenyl acetic acid with mono- or polyhydric alcohols, e.g. with methanol, ethanol, octanol, octadecanol, 1,6-hexanediol, 1,9-nonanediol, ethylene glycol, 1,2-propanediol, neopentyl glycol, thiodiethylene glycol, diethylene glycol, triethylene glycol, pentaerythritol, tris(hydroxyethyl)isocyanurate, N,N′-bis(hydroxyethyl)oxamide, 3-thiaundecanol, 3-thiapentadecanol, trimethylhexanediol, trimethylolpropane, 4-hydroxymethyl-1-phospha-2,6,7-trioxabicyclo[2.2.2]octane.

Examples of amides of β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid include N,N′-bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hexamethylenediamide, N,N′-bis(3,5-di-tert-butyl-4-hydroxy-phenylpropionyl)trimethylenediamide, N,N′-bis(3,5-di-tert-butyl-4-hydroxyphenylpropionyl)hydrazide, N,N′-bis[2-(3-[3,5-di-tert-butyl-4-hydroxyphenyl]propionyloxy)ethyl]oxamide.

Examples of aminic antioxidants include N,N′-di-isopropyl-p-phenylenediamine, N,N′-di-sec-butyl-p-phenylenediamine, N,N′-bis(1,4-dimethylpentyl)-p-phenylenediamine, N,N′-bis(1-ethyl-3-methylpentyl)-p-phenylenediamine, N,N′-bis(1-methylheptyl)-p-phenylenediamine, N,N′-dicyclohexyl-p-phenylenediamine, N,N′-diphenyl-p-phenylenediamine, N,N′-bis(2-naphthyl)-p-phenylenediamine, N-isopropyl-N′-phenyl-p-phenylenediamine, N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine, N-(1-methylheptyl)-N′-phenyl-p-phenylenediamine, N-cyclohexyl-N′-phenyl-p-phenylenediamine, 4-(p-toluenesulfamoyl)diphenylamine, N,N′-dimethyl-N,N′-di-sec-butyl-p-phenylenediamine, diphenylamine, N-allyldiphenylamine, 4-isopropoxydiphenylamine, N-phenyl-1-naphthylamine, N-(4-tert-octylphenyl)-1-naphthylamine, N-phenyl-2-naphthylamine, octylated diphenylamine, 4-n-butylaminophenol, 4-butyrylaminophenol, 4-nonanoylaminophenol, 4-dodecanoylaminophenol, 4-octadecanoylaminophenol, bis(4-methoxyphenyl)amine, 2,6-di-tert-butyl-4-dimethylamino-methylphenol, 2,4′-diaminodiphenylmethane, 4,4′-diaminodiphenylmethane, N,N,N′,N′-tetra-methyl-4,4′-diaminodiphenylmethane, 1,2-bis[(2-methylphenyl)amino]ethane, 1,2-bis(phenylamino)propane, (o-tolyl)biguanide, bis[4-(1′,3-dimethylbutyl)phenyl]amine, tert-octylated N-phenyl-1-naphthylamine, a mixture of mono- and dialkylated tert-butyl/tert-octyldiphenylamines, a mixture of mono- and dialkylated nonyldiphenylamines, a mixture of mono- and dialkylated dodecyldiphenylamines, a mixture of mono- and dialkylated isopropyl/isohexyldiphenylamines, a mixture of mono- and dialkylated tert-butyldiphenylamines, 2,3-dihydro-3,3-dimethyl-4H-1,4-benzothiazine, phenothiazine, a mixture of mono- and dialkylated tert-butyl/tert-octylphenothiazines, a mixture of mono- and dialkylated tert-octyl-phenothiazines, N-allylphenothiazine, N,N,N,N′-tetraphenyl-1,4-diaminobut-2-ene.

The lubricant of the present invention may be made according to the procedure shown in FIG. 2. The partially-esterified sucrose is produced with sucrose and refined vegetable oils, such as soybean oil or cotton seed oil. As stated above, a sucrose molecule contains eight potential esterification sites, each of which may support a fatty acid of up to about 28 carbon atoms. Although any single sucrose molecule may form from 1-8 ester linkages with a fatty acid, the average distribution found to be beneficial for the method of lubricating described herein has from 5-7 esters, and preferably from 6-7 esters. The average distribution is most preferably a 6 ester sucrose polyester, i.e, on average, six fatty acid molecules are bound through an ester linkage to a sucrose molecule backbone.

Typical distribution examples are provided in Table 1 below, wherein SE means sucrose ester, the number following SE means the number of fatty acid chains bound to the sucrose and I-BAR means the average degree of esterification.

TABLE 1 Distribution Examples SEFA Formulations SE 1 SE 2 SE 3 SE 4 SE 5 SE 6 SE 7 SE 8 I-BAR 1618U 0.0 0.0 0.0 0.0 1.0 5.4 20.0 73.6 7.61 1618U 0.0 0.0 0.0 0.0 0.3 0.4 20.5 78.6 7.76 1618U B6 0.0 0.4 1.3 7.3 15.9 25.2 28.9 21.1 6.10 1618U B6 0.1 0.4 2.3 8.8 17.9 26.1 29.3 15.2 5.88

Ester distribution can be obtained by SuperCritical Fluid Chromatography (SFC) or HPLC with SE representing the Sucrose Esters with 1-8 fatty chains attached and I-BAR being a calculated average number of fatty chains.

The 6-ester sucrose polyester has been found to provide the best overall viscosity and the best bonding to the metal surfaces in use.

In various embodiments, an antioxidant as described above may be added to the partially-esterified sucrose. From about 20 ppm to about 10,000 ppm of one or more of the antioxidants described above may be added to the partially-esterified sucrose composition. For example, about half of the added antioxidant may be an active tocopherol in combination with one or more additional antioxidants.

The addition of an antioxidant increases the oxidative stability of the lubricant. Fats and oils are susceptible to oxidative degradation. Thus, the addition of an amount of an antioxidant effective for minimizing oxidation of the partially-esterified sucrose increases the useful life of the lubricant.

In use, the lubricant is applied to the surfaces of machinery in need of lubrication by any suitable known means, including without limitation application by hand using, for example, a cloth, sponge or brush applicator, application by spraying or squirting onto the desired surface. The amount of lubricant applied will vary depending on the tool, the intended period of use and the environment in which the tool is used.

When used to lubricate pneumatic tools, the lubricant may be added to a reservoir in fluid communication through a venturi or another valve, with the compressed air flow. In some tools, the lubricant may be pre-loaded into a lubricator, essentially, a replaceable reservoir for the lubricant.

Referring to FIG. 1, the boundary lubrication in a dynamic mechanical system is primarily governed by the formation of a stable tribochemical film. Without being bound by any particular theory the lubricant of the present invention appears to line up in a uniform fashion along exposed surfaces of the metal and the orientation of the lubricant is believed to be responsible, at least in part, for the significant improvement in wear resistance and lubrication under extreme pressure demonstrated by the lubricant composition of the present invention. The orientation of the lubricant may also be responsible for there not being a greasy feel to the lubricant when applied to metal surfaces due, it is believed, to better metal adhesion over conventional lubricants obtained by the lubricant of the present invention.

In contrast, traditional rock drill oils are easily wiped away as the tools' metal surfaces pass over each other, as a tool passes over the metal surface of a work piece, or when pressurized air in an air-driven tool passes over the lubricated metal, as schematically represented in part (b) of FIG. 1. It is necessary to continually replace the rock drill oil to maintain a film of the coolant between the tool and work piece. To compensate, many operators over-inject traditional rock drill oils, as a safe way to avoid tool failure.

Tests to assess the viability of vegetable oil based lubricants were conducted. The results are shown in Table 2 below.

TABLE 2 Vegetable Oil Based Lubricants Product Tool Life Fog Odor Cost Overall Result Castor Oil Excellent Very little Low Low Some operators with Special complained of irritation. lubricator Others didn't mind it. RBD Excellent Problematic French Fries Low A robust lubricator could Canola Oil odor not be found that could minimize the canola flow enough, and viscosity modifying additives were expensive. Lubrizol ® Excellent None None Very High Excellent result overall Synester but price was unacceptable. GY-25 ester Uniqema Excellent None None Very High Excellent tool life and Priolube ® operator acceptance but complex esters price was very high.

The conclusion after running the aforementioned lubricants in mining operations over several months was that vegetable oils and esters outperformed petroleum oils by far in terms of tool life and consumption, but the Lubrizol and Uniqema esters in particular were too expensive and the castor oil and RBD canola oils resulted in unacceptable fogging, or required special applicators to prevent fogging, irritated workers or had an unpleasant odor.

When tests were done comparing the partially-esterified sucrose based lubricants to other vegetable based lubricants, all of the problems experienced with either petroleum based or vegetable oil based lubricants were avoided.

EXPERIMENTS Partially-Esterified Sucrose Based Lubricant

1. Four Ball Wear Test. A standard Four Ball Wear Test was conducted. The Four Ball Wear Test puts one rotating ball against three fixed balls under specific conditions of pressure, temperature, revolutions per minute and duration. The test is used to evaluate the friction- and wear-control ability of greases and lubricating oils in sliding steel-on-steel applications. The point contact interface is obtained by rotating a 12.7 mm diameter steel ball under load against three stationary steel balls immersed in the lubricant. The normal load, frictional force, and temperature are monitored using commercially available software. The rotating speed, normal load, and temperature can be adjusted in accordance with published ASTM standards. For evaluating wear preventive characteristics of lubricants, the subsequent wear scar diameters on the balls are measured. For evaluating the load-carrying capacity of lubricants, the normal load at which welding occurs at the contact interface can be recorded.

The lubricating properties of partially-esterified sucrose based lubricant using the Four Ball Wear Test resulted in a 0.35 mm scar with a 40 Kg. load after one hour. A comparison with one of the most commonly used lubricant's (Petro Canada's Ardee 150) resulted in a 0.4 mm scar with a 20 Kg. load after one hour.

2. Copper Tapping. Tests conducted on tapping elemental copper demonstrated that one embodiment of the partially-esterified sucrose based lubricant, SEFA 1618S, outperformed Tapping Fluids based on chlorine extreme pressure additives. Copper Tapping tests are based on the Cincinnati Machine Thermal Stability Test wherein polished, pre-weighed steel and copper rods are immersed in a beaker containing 200 cc of oil and heated to 135° C. for 168 hours. The rods are weighed and examined for discoloration and weight loss. Elemental copper is extremely ductile, and poor lubricity results in torn threads (rejects). SEFA excelled in all tests. The comparison is shown in Table 3 below.

TABLE 3 Comparative Copper Weight Change of SEFA with those of Other Esters & Base Oils TE1 Ester SPE3 UPE2 HVI PAO DE3 (Trimellitate (Saturated (unsaturated (mineral (Poly alpha SEFA (Diester) Ester) polyol ester) polyol ester) oils) olefin) 1618S Copper Weight 0.01 0.06 0.06 0.05 <0.01 <0.01 0.03 Change, % Loss The composition of SEFA1618S (IV = 85) is the same as the composition of SEFA1618U (IV = 130) except for differences in the Iodine Value (IV). See the ester distribution for SEFA 1618U in Table 1 above.

3. On Site Testing. The partially-esterified sucrose based lubricant was tested as the sole lubricant for two drills in a mine to determine how it would perform in an enclosed environment on actual equipment. The drills were used to create a vent raise to the surface. Drilling was overhead and blasting of the material was carried out above the drills. When the ceiling was blasted down, comparative drilling resumed on the blasted rock to drill. There is virtually no ventilation in this environment, arguably the worst condition possible to test in. Two drills were lubricated with partially-esterified sucrose based lubricant. Additional drills were lubricated with a conventional lubricant, Petro Canada's Ardee 150 Rock Drill Oil. The tests were conducted over a period of 3-5 months.

Observations:

The drills lubricated with the partially-esterified sucrose based lubricant used only 35-40% of the amount of conventional rock drill fluid used on the comparative drills. The amount of lubricant was reduced to even lower levels compared to the conventional lubricant amounts needed during the same period. It is believed that a reduction to 25% consumption for the partially-esterified sucrose based lubricant as compared to Petro Canada's Ardee 150 Rock Drill Oil will provide effective lubrication.

The drills that were lubricated with partially-esterified sucrose based lubricant did not have to be changed during the period of the trial while the drills lubricated with conventional lubricants had to be rebuilt 1 to 2 times at an average cost of $3400.00 per drill.

It is known that prior art oils sometimes freeze in the tool exhaust port due to water in compressed air freezing upon exit. It is then necessary to stop the tool and chip the ice away from the exhaust port. No freezing was experienced with the partially-esterified sucrose based lubricant during the trial period.

It is known that prior art oils make the operators' exposed skin and clothing black by shift's end. No staining or soiling of skin or clothing was experienced by those using the drills lubricated with partially-esterified sucrose based lubricant during the trial period.

It is known that prior art oils make the drill slippery, making it often necessary for miners to stop work to rub gloves with rock drill fines to get a grip. There were no slippery deposits found on the tools using partially-esterified sucrose based lubricant. Moreover, fogging of the lubricant was virtually eliminated.

The drills lubricated with the poly-esterified sucrose based lubricant always sounded well lubricated during the trials. At times during the trial, the large amount of water in the compressed air of the tools lubricated with the conventional lubricant (Ardee 150), which has an emulsifier in it, would cause the conventional lubricant to become too thin, thereby exposing the tools to the danger of burning up. Operators were forced to increase the oil injection, which is believed to have been at least one cause of the fogging and associated discomfort experienced with the conventional lubricants.

TABLE 4 Comparisons of Rock Drill Oils/Greases with partially-esterified sucrose based lubricant (SEFA 1618 S) SEFA Ardee 150 Fully Rock Drill Vultrex EP000 Veg. Oils Product esterified Oil Grease Various V. Index* 169 92  94 140-200 TLV** (ppm) <2  5+ <2 2-5 Fogging 2 3 1 4 Worst Tool Life 1 Best 4 3 2 Odor 1 4 3 2 Consumption 1 4 2 3 Washout 1 4 3 2 Operational 1 4 2 3 Due to High Costs Materials cost *The Viscosity Index, commonly designated VI, is an arbitrary numbering scale that indicates the changes in oil viscosity with changes in temperature. Viscosity index can be classified as follows. Low VI - below 35 Medium VI - 35 to 80 High VI - 80 to 110 Very High VI - 110 to 125 Super VI - 125 to 160 Super High VI - above 160 to 200 **TLV—Threshold Limit Value is a measure of the weighted average concentration to which it is believed that nearly all workers may be repeatedly exposed, day after day, without adverse effects.

Fogging and odor were evaluated subjectively using a scale of 1-4, with 4 being the worst and 1 the best observed results.

Tool life was determined by field test comparison and is based on a scale of 1-4, wherein 1 means longest wear life and 4 means shortest wear life.

Washout means cleaning of the tool using water and was determined by the amount of residue left on the tool.

Consumption means the amount of lubricant used in the tool and was determined by the amount of times the lubricator needed to be refilled.

In tests run with the embodiment of the lubricant having an average distribution of 6 fatty acid esters bound to the sucrose backbone, the values improved even more over the fully esterified embodiment having 8 fatty acids bound to the sucrose backbone. For example, there was no visible fogging, so the 6-ester embodiment had a fogging score of 1.

The partially-esterified sucrose based lubricant of the present invention has been found to reduce product consumption by as much as 75% compared to the conventional lubricants tested. The partially-esterified sucrose based lubricant has a high threshold limit value (TLV) of 10 ppm, making it much safer for workers than the conventional lubricants. The partially-esterified sucrose based lubricant has better lubricity and tool protection than any petroleum based lubricant. It reduces tool rebuild costs for end user.

The partially-esterified sucrose based lubricant is non fogging, a factor that is very important to worker safety and comfort as well as to avoidance of work stoppage to compensate for slippery tool surfaces. The partially-esterified sucrose based lubricant biodegradable and has considerably lower production costs than petroleum based oils and some vegetable based oils. Further, the partially-esterified sucrose based lubricant is useful as a chain saw oil, conveyor chain lubricant, wire rope lubricant for elevating devices, metalworking, such as tapping, threading and drilling, saw guide oil, such as those used for band saws in lumber production, form release oil for the construction industry, water pump gear case oil, gear oil, and a railroad rail oil used on curves to minimize wear.

The dimensions and values disclosed herein are not to be understood as being strictly limited to the exact numerical values recited. Instead, unless otherwise specified, each such dimension is intended to mean both the recited value and a functionally equivalent range surrounding that value. For example, a dimension disclosed as “40 mm” is intended to mean “about 40 mm.

Every document cited herein, including any cross referenced or related patent or application, is hereby incorporated herein by reference in its entirety unless expressly excluded or otherwise limited. The citation of any document is not an admission that it is prior art with respect to any invention disclosed or claimed herein or that it alone, or in any combination with any other reference or references, teaches, suggests or discloses any such invention. Further, to the extent that any meaning or definition of a term in this document conflicts with any meaning or definition of the same term in a document incorporated by reference, the meaning or definition assigned to that term in this document shall govern.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of this invention. 

1. A lubricating composition for lubricating at least two metal surfaces which are in a frictional relationship, the lubricating composition comprising a mixture of: (1) a partially-esterified oligosaccharide; and (2) an effective amount of an antioxidant for reducing oxidation of the partially-esterified oligosaccharide.
 2. The lubricating composition recited in claim 1 wherein the partially-esterified oligosaccharide comprises a sucrose backbone having an average distribution of bound fatty acids from 5 to
 7. 3. The lubricating composition recited in claim 2 wherein the partially-esterified sucrose molecules have an average distribution of 6 to 7 fatty acids bound thereto.
 4. The lubricating composition recited in claim 2 wherein each fatty acid bound to the sucrose backbone has from 2 to 28 carbon atoms in unbranched or branched chains.
 5. The lubricating composition recited in claim 1 comprising from about 20 to about 10,000 ppm of the antioxidant.
 6. The lubricating composition recited in claim 1 wherein the antioxidant is selected from the group consisting of tocopherols, alkylated monophenols, alkylthiomethylphenols, alkylidenebisphenols, hydroxylated thiodiphenyl ethers, hydroquinones and alkylated hydroquinones, hydroxybenzylated malonates, benzyl compounds, aromatic hydroxybenzyl compounds, triazine compounds, benzyl phosphonates, acylaminophenols, ascorbic acid, certain esters, and aminic antioxidants and mixtures thereof.
 7. The lubricating composition recited in claim 6 wherein at least half of the antioxidant is an active tocopherol.
 8. The lubricating composition recited in claim 1 wherein the partially-esterified sucrose molecules have an average distribution of about 6 fatty acids bound thereto, the fatty acids are branched or unbranched chains each having from 4 to 28 carbon atoms and at least half of the antioxidant is an active tocopherol.
 9. A method of reducing friction between at least two metal surfaces which are in a frictional relationship with each other comprising the step of contacting the metal surfaces with an effective amount of a lubricant composition comprising partially-esterified oligosaccharide molecules.
 10. The method recited in claim 9 wherein the partially-esterified oligosaccharide molecule comprises a sucrose backbone having an average distribution of from 5 to 7 fatty acids bound thereto.
 11. The method recited in claim 10 wherein each fatty acid bound to the sucrose backbone has from 2 to 28 carbon atoms in unbranched or branched chains.
 12. The method recited in claim 11 wherein the fatty acids bound to the sucrose backbone have from 4 to 22 carbon atoms in unbranched or branched chains.
 13. The method recited in claim 10 wherein said partially-esterified sucrose molecules have an average distribution of 6 to 7 fatty acids bound thereto.
 14. The method recited in claim 13 wherein said partially-esterified sucrose molecules having an average distribution of about six fatty acids bound thereto.
 15. The method recited in claim 9 wherein the lubricant further comprises an amount of an antioxidant effective for reducing the rate of oxidation of the lubricant.
 16. The method recited in claim 15 wherein the lubricant from about 20 to about 10,000 ppm of an antioxidant.
 17. The method recited in claim 15 wherein the antioxidant is selected from the group consisting of tocopherols, alkylated monophenols, alkylthiomethylphenols, alkylidenebisphenols, hydroxylated thiodiphenyl ethers, hydroquinones and alkylated hydroquinones, hydroxybenzylated malonates, benzyl compounds, aromatic hydroxybenzyl compounds, triazine compounds, benzyl phosphonates, acylaminophenols, ascorbic acid, certain esters, and aminic antioxidants and mixtures thereof.
 18. The method recited in claim 17 wherein at least half of the antioxidant is an active tocopherol.
 19. The method recited in claim 9 wherein contacting the metal surfaces comprises introducing the lubricant into the flow of compressed air in a pneumatic tool.
 20. The method recited in claim 9 wherein contacting the metal surfaces comprises applying the lubricant directly to the metal surfaces in need of lubrication. 